Transmission line spacer



1944- c. 1.. ROUAULT 2,355,111

TRANSMISSION LINE SPACER Filed May 14, 1942 Inventor: Charles L. Rouaulo,

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Patented Aug. 8, 1944 TRANSMISSION LINE SPACER Charles L. Rouault, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application May 14,1942, Serial No. 442,895

1 Claim.

My invention relates to concentric transmission lines, and more particularly to means for holding the conductors of such concentric lines in properly spaced relation with respect to each other. 7

It is common to use centrally apertured discshaped insulating members between the central conductor and the cylindrical concentric outer conductor of a concentric transmission line to maintain the two conductors in properly spaced relation. It is an object of my invention to provide new and improved means for maintaining such disc-shaped members properly positioned within the concentric transmission line.

It is a corollary object of my invention to provide new and improved means for maintaining such disc-shaped members properly positioned within such a transmission line and which, in cooperation with such disc-shaped members of a particular cross-section, minimizes the losses in the line.

The features'of my invention which I believe to be novel are set forth with particularity in the appended claim. "My invention itself, both as to its organization and manner of operation-togather with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a cross-sectional view taken along an axis of a concentric transmission line, and Fig. 2 is a cross-sectional view taken perpendicular to such axis along the section line 22 in Fig. 1.

In Fig. 1 a central tubular conductor I0 is placed coaxially within an outer cylindrical conductor II, and is maintained in proper spaced relation thereto by a centrally apertured discshaped insulating member I2. As shown in the figure, the member I2 is relatively thin near the outer conductor II, and is thicker at positions nearer the central conductor ID.

The insulating member I2 is so formed, thin at its outer periphery and thicker towards its inner portion, that the energy loss per unit volume within the insulating member I2 is uniform through the material of member I2. That is, flux density within the material of insulating member I2 is uniform at all points. Such a shape, providing such uniform flux density and power loss per unit volume in member I2, minimizes the probability of breakage of member I2 by high voltages existing between conductors I6 and II.

The flux density and energy loss per unit volume in such an insulator may be made substantially uniform throughout it if the area within member I2 cut by a cylinder concentric with conductor I0 be the same, no matter what the diameter of the cylinder may be. Expressed otherwise, the product of each radius and the thickness of insulating member I2 in a direction parallel to conductor ID at such radius is constant at all radii.

Breakage of insulation is caused by local heating, and, if the energy loss per unit volume is constant throughout the material of the insulator, the probability of breakage is equal at all points thereof and is consequently minimized for the insulation asa whole, total energy losses remaining the same. I

The above described construction of the insulating member I2 is theoretically correct only if all the electric flux entering the insulating member I2 adjacent the conductor II'I passes en tirely through the member I2 and from thence into the conductor II. Since, however, the electric flux tends to pass between the conductors I0 and II perpendicularly to the axes thereof, some of the electric flux which passes into the insulating member I2 from the conductor III passes out of the insulating member I2 through its side surfaces I4 before reaching the conductor II. Therefore, the total flux passing from the conductor Ill into the insulating member I2 is greater than the total flux passing from the in sulator I2 into the conductor I I. Consequently, the outer periphery of the insulating member I2 may be made somewhat thinner, or the inner part somewhat thicker, in the axial direction of the transmission line than would otherwise be expected. The proper dimensions of the insulating member I2, as thus modified, depend on the relative dielectric constant of the material of the insulating member I2 and of the medium surrounding it between the conductors I0 and II.

To maintain the insulating member I2 fixed in one position along the conductor II), a special arrangement is utilized. The inner cylindrical surface I5 0f the insulating member I2 adjacent the conductor I0 is cut away, as by routing or undercutting, to form a semi-toroidal recess I6 whose major plane is perpendicular to the axes of the conductors III and II. The cross-section of this recess I6 may, if desired, be that of a semi-circle, or of other similar shape, designed to distribute electrical stress uniformly through the insulating member I2.

A metal coating 11 is applied, as by electroplating or spraying, to the surface of the toroidal recess I6. Silver is preferably used for this metal coating I'I.

Two rounded metal cuplike members I8, pressed apart by a, helical spring l9, are placed within the tubular conductor I through holes out through opposite walls of the conductor I0. The spring is biases these members l8 outwardly and into the metal covered recess IS in the insulating member I2, thereby locking the member 12 adjacent the holes 20.

The metal cup members 18 should fit snugly against the metal coating H to minimize the formation of corona. To this end, the cross sections of the cup members I8 are made the same as the cross sections of the recess I6.

To assemble the insulating member l2 with its locking means, the member 12 is first slid along the conductor I0 until it is near the holes 20, but to one side thereof. Next, the metal cup members l8 are placed over the opposite ends of the spring [9 and pushed through the holes 20, the members l8 being pressed down so that they do not project outside of the conductor I 0. Next, the insulating member I2 is slipped over the hole 20, the metal cuplike members l8 being released as the insulating member 12 passes over them. As the insulating member I2 is slid over the holes 20, the metal members 18 spring outwardly into the recess I 6, and thus lock the members 12 in position.

It is important that the cross sections of the members I8 when they pass through the conductor I0 be substantially perpendicular to the walls of conductor ll]. Given that relation, the members it offer maximum resistance to displacement from recess l6 by forces exerted along conductor ID.

The semi-toroidal form of the metal coating I! tends to distribute the electric flux proceeding from the conductor l0 into the insulating member l2 evenly. It is important that there be no sharp projections or points on which a concentration of such electric flux can exist. The presence of the rounded conducting surface I! within the body of member 12 changes the flux distribution within the member l2, making it desirable to make member l2 somewhat thicker than described above at short distances from conductor H).

In Fig. 2 the shape of various parts of the insulator l2 and the locking means may be clearly seen. In this figure, like reference numerals are applied to like parts. The disc-like form of the insulating member [2 is shown clearly, and the semi-toroidal recess IS with the metallic coating I1 is shown in dotted lines. The rounded form of the cuplike members l8 may also be clearly seen, these members being shown in dotted lines within the insulating member 12, and it may also be observed how these members l8 project through opposite holes 20 in the conductor l 0 and within the recess H5 in the member 12.

It is apparent from Fig. 2 that force can not be transmitted from member 12 to members l8 except in a direction parallel to conductor In. This is true because the semi-toroidal form of the recess 16 allows insulator l2 to rotate more or less freely around conductor ID with only frictional resistance offered by cup members l8. This is of advantage because the walls of cup members l8 are truly perpendicular to the walls of conductor I 0 only in those directions in which force can be transferred therebetween.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects and I therefore aim in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

In combination, a conductor having a hole transversely therethrough, a tubular conductor concentric therewith, means for supporting said first conductor concentrically within said tubular conductor comprising an annular insulator having a surface fitting closely around said first conductor, said insulator having a semi-toroidal recess in said surface, locking means for permanently maintaining said insulator in fixed position along said inner conductor comprising a pair of metallic members in said hole, each of said members having a shape whose cross-section conforms to the cross-section of said recess and is larger than said recess, means for pressing said members partly out of opposite ends of said hole and into said recess in said insulator, said metallic members remaining partly in said hole and thereby preventing relative movement between said insulator and said inner conductor, and a conductive coating on the walls of said recess effective to distribute electrical stress uniformly through said surface, the shape of said insulator being such that energy loss per unit volume therewithin is substantially uniform to reduce the likelihood of breakage.

CHARLES L. ROUAULT. 

